Tailoring thermoelectric properties of nanostructured crystal silicon fabricated by infrared femtosecond laser direct writing

Abstract

The periodic nanostructuring of inner part of semiconductors can be successfully accomplished by the infrared ultrashort pulse laser with a double pulse configuration. Self‐organized nanostructures inside semiconductor could be induced empirically only if it is indirect band gap semiconductor. The strained silicon regions with a width of about 100 nm are self‐aligned parallel to the polarization direction of the first arriving pulses, despite of the polarization direction of the secondly arriving pulses. AFM inspections reveal that such strained silicon nanostructures exhibit high electric conductivity and low thermal conductivity. The formation mechanisms would be interpreted in terms of the electrostrictive force through the interaction between electron‐hole plasma and phonon. Apart from the basic understanding, such nanostructured silicon will open the door to the fabrication of the self‐contained thermoelectric devices.

Origin of Waveguiding in Ultrashort Pulse Structured Silicon

“…They demonstrated the generation of polycrystalline and amorphous silicon at silicon surfaces affected by ns, ps, and fs laser pulses, respectively. Likewise Mori et al., who study nanogratings in Si, see the same behavior in their Raman measurements. Peak‐fitting of the crystalline contribution at 520 cm −1 with a Lorentzian shape and a Gaussian shape for the amorphous contributions at 480 cm −1 as well as for the grain boundaries contributions at 500 cm −1 yield information on the degree of crystallinity .…”

“…Within the last two decades, numerous attempts have been performed to overcome these limitations . Recently, localized modifications in the bulk of silicon using ultrashort laser pulses have been demonstrated . This resulted in the first demonstration of waveguides written with fs laser pulses at a wavelength of 1550 nm by Pavlov et al .…”

“…[9][10][11][12] Recently, localized modifications in the bulk of silicon using ultrashort laser pulses have been demonstrated. [13][14][15] This resulted in the first demonstration of waveguides written with fs laser pulses at a wavelength of 1550 nm by Pavlov et al [16] This year, we presented a detailed characterization of sub-ps written waveguides regarding near field distribution, scattering characteristics, and damping losses. [17] DOI: 10.1002/lpor.201800268…”

Limitations to laser machining of silicon using femtosecond micro-Bessel beams in the infrared

“…However, despite the steep angular components forming our beam (>20 ), we measure that the clamping of the intensity, the subsequent free-carrier density and absorbed energy remain at levels far below the thresholds for local modification in bulk silicon. There is today a general trend toward ultrashort pulses for ultraprecision micromachining applications but our investigations with SWIR femtosecond Bessel beams suggest that only longer pulses 11,12 or multiple pulses 13 can be envisioned for deep micromachining inside silicon.…”

The Fabrication of Micro/Nano Structures by Laser Machining

“…Periodic nanostructures within the semiconductor can be achieved by an infrared ultrashort pulse laser with a dual pulse configuration. In 2015, M. Mori et al reported that the periodic nanostructures inside the semiconductor caused by infrared ultrashort pulse lasers were generated by a double pulse configuration without surface damage [187]. In 2015, M. Sobhani et al studied irradiated sub-micro/nano structure of polished silicon using double nanosecond laser pulses (λ = 532 nm) in distilled water.…”